1. Field of the Invention
The present invention relates to a magnetic head and a magneto-optical recording apparatus, and more particularly to a magnetic head and a magneto-optical recording apparatus for recording an information signal in a magneto-optical recording medium such as a magneto-optical disk.
2. Related Background Art
There are well known magneto-optical recording apparatus for recording an information signal in high density in a magneto-optical recording medium such as a magneto-optical disk.
FIG. 1 is a schematic structural drawing of a magneto-optical recording apparatus. In FIG. 1, reference numeral 1 designates a disk as a magneto-optical recording medium, in which a magnetic recording layer 1a is formed. The disk 1 is rotation-driven by a spindle motor 2. A magnetic head 3 is disposed on the top face side of disk 1 with an optical head 4 on the bottom face side thereof. The magnetic head 3 is held on the tip of suspension 5, and fixed ends of optical head 4 and suspension 5 are connected by an interconnecting member 6.
For recording the information signal in the magnetic recording layer 1a of disk 1 by the above magneto-optical recording apparatus, while rotating the disk 1 at high speed by the spindle motor 2, laser light 8 is projected through an objective lens 9 in the optical head 4 onto a recording track formed in a spiral form on the magnetic recording layer 1a. The laser light 8 is focused on the recording track, and focusing control and tracking control are performed with the objective lens 9 in order to keep the laser light 8 accurately following up the recording track.
At a portion illuminated by the laser light 8 on the magnetic recording layer la the temperature rises up to above the Curie temperature thereof. At the same time, the magnetic head 3 applies a bias magnetic field modulated according to the information signal to the portion illuminated by the laser light 8. This causes the orientation of magnetization in the temperature-rising portion of the magnetic recording layer 1a to be aligned along a direction of the bias magnetic field during a process of a decrease in temperature as the portion moves away from the portion illuminated by the laser light 8 with rotation of disk 1. In this manner the information signal is recorded on the recording track by a change of orientation of magnetization.
Next, FIGS. 2A to 2C show the construction of a magnetic head for magneto-optical recording used in such a magneto-optical recording apparatus. Here, FIG. 2A is a back view, FIG. 2B a bottom view, and FIG. 2C a side view. In the drawings, reference numeral 10 denotes a U-shaped core, which is normally made of a high-permeability ferrite. Further, numeral 11 represents a coil provided for the core 10. The magnetic head is provided with a slider 12 having an aerodynamic shape of a floating surface in order to float and run to maintain a fine gap relative to the disk by an air flow caused by high-speed rotation of the disk. Generally, the slider 12 is made of a non-magnetic ceramic material. A nearly square pole-tip face 10a is formed at one end of the core 10, and the core 10 and slider 12 are bonded to each other with the pole-tip face 10a being set on the bottom face side of the magnetic head.
In the above magnetic head, the bias magnetic field is generated approximately normal to the pole-tip face 10a therefrom when an electric current flows in the coil 11. Accordingly, the magnetic head is so arranged that the bottom face thereof is opposed to the disk and the portion illuminated by the laser light on the magnetic recording layer is located immediately below the pole-tip face 10a.
FIG. 3 is a graph to show a relationship between recording current flowing in the coil and magnetic field generated by the magnetic head in the case of the conventional magnetic head for magneto-optical recording. Here is shown an example of the conventional, standard magnetic head, in which the core is made of a ferrite the saturation magnetic flux density of which is 5 kG, in which the dimensions of the pole-tip face are 0.15 mm.times.0.15 mm, and in which the number of windings of the coil is 20. Here, the bias magnetic field of 200 to 300 (Oe) is normally applied in order to perform signal recording in a good condition on the magneto-optical disk. As seen from this graph, the magnetic field generated is in proportion to the recording current in the range of small recording currents, but the magnetic field generated is saturated sooner or later with an increase of recording current. This is because the magnetic flux density inside the core cannot increase over the saturation magnetic flux density of ferrite.
In addition, the magnitude of the saturation magnetic field depends upon the frequency f of a recording signal, as shown: the saturation magnetic field shows a trend to decrease with an increase of frequency f. This phenomenon results from the fact that with higher frequencies f of a recording signal a high-frequency loss (which is mainly a characteristic property of the magnetic material making the core) in the magnetic head increases so as to heat the magnetic head and with heating the saturation magnetic flux density of the ferrite making the core decreases. FIG. 4 shows an example of temperature dependence of saturation magnetic flux density Bs of the ferrite used for the core in the conventional magnetic head for magneto-optical recording. As shown, the saturation magnetic flux density Bs of ferrite is 5 kG at ordinary temperature (25.degree. C.), but decreases with an increase of temperature, becoming about 3 kG at 100.degree. C.
Meanwhile, the magneto-optical recording apparatus as described is recently demanded to increase the speed of signal recording, which requires an increase in frequency of the recording signal. However, as described above, the saturation magnetic field decreases because of the increase of high-frequency loss in the magnetic head with higher frequencies of recording signal. For example, as shown in FIG. 3, in a case of the frequency of the recording signal being over 10 MHz, it is impossible to obtain a magnetic field generated above 200 (Oe) necessary for satisfactory signal recording no matter how much the recording current is increased. As described, the conventional apparatus had a problem that higher-speed signal recording was impossible, because the frequency of recording signal was limited by performance of the magnetic head.
Additionally, the above magnetic head has a large inductance of a coil as 1.0 to 1.5 .mu.H. Accordingly, in order to supply a high-frequency current to the coil, a high voltage needs to be supplied to the coil, which increases dissipation power of a drive circuit of the magnetic head. Such a restriction also keeps the frequency of recording signal from being increased above 10 MHz, raising a problem of incapability of faster signal recording.